This invention relates generally to the field of integrated circuits and more particularly to a method and system for dynamic compensation.
Integrated circuits often employ a variety of amplifiers, such as voltage regulators, to increase or decrease voltage levels within the integrated circuit. Amplifiers often have at least two poles in their frequency response that are associated with gain and phase behavior. Gain and phase behavior depends upon the circuit design of the amplifier, and can depend upon load circuitry associated with the amplifier.
Conventional amplifier circuits, including voltage regulators, may include an output stage that resembles a class A amplifier stage. Such designs are limited by the output storage capacitance of the circuit. Other designs may employ a class B output configuration with a generally low impedance output and internal compensation to maintain the amplifier within an operable range. Many of these circuit designs are used in applications or with loads having a range of transistor current requirements and load characteristics. However, these designs are often not able to maintain the amplifier within an operable range for these applications or for loads having varying requirements.
Amplifiers using field effect technology generally have high output impedance and the pole contributed by the output load is generally located at a relatively low frequency. Without a zero between the first two poles in the amplifier""s frequency response, instability can result. Existing compensation schemes depend on the characteristics of the load. The location of the zero and one or more poles can be affected by the load, if the pole moves due to output load characteristics such that the zero designed into the frequency response for stability is no longer between the first two poles of the amplifier""s frequency response. Thus, designing stable amplifiers is difficult without knowing beforehand the load characteristics. Often, however, load characteristics may not be known. Therefore, a system and method is needed to provide effective dynamic compensation for amplifier applications in integrated circuits.
One aspect of the invention is an integrated circuit comprising an amplifier having at least two poles in its frequency response and an output impedance compensation circuit coupled to an output node of the amplifier. The output impedance compensation circuit is operable to create a feedback signal proportional to the impedance of an output load coupled to the output node, and create a zero in the frequency response of the amplifier in response to the feedback signal between the at least two poles.
The invention provides several important advantages. Various embodiments of the invention may have none, some, or all of these advantages. The invention allows amplifiers in integrated circuits to operate stably under a wide variety of output load conditions. Generic amplifier designs, including voltage regulator designs, may thus be done without detailed knowledge of output load characteristics. Such amplifiers may have reduced circuit area in comparison to amplifiers with other compensation schemes, and may have improved power consumption.